Network Working Group C. Daboo
Internet-Draft Apple Inc.
Updates: 4791,5546 (if approved) B. Desruisseaux
Intended status: Standards Track Oracle
Expires: October 4, 2012 April 2, 2012
CalDAV Scheduling Extensions to WebDAVdraft-desruisseaux-caldav-sched-12
Abstract
This document defines extensions to the CalDAV "calendar-access"
feature to specify a standard way of performing scheduling operations
with iCalendar-based calendar components. This document defines the
"calendar-auto-schedule" feature of CalDAV.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 4, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Internet-Draft CalDAV Scheduling Extensions April 20121. Introduction
This document specifies extensions to the CalDAV "calendar-access"
[RFC4791] feature to enable scheduling of iCalendar-based [RFC5545]
calendar components between calendar users.
This extension leverages the scheduling methods defined in the
iCalendar Transport-independent Interoperability Protocol (iTIP)
[RFC5546] to permit calendar users to perform scheduling operations
such as schedule, reschedule, respond to scheduling request or cancel
calendar components, as well as search for busy time information.
However, the following iTIP [RFC5546] features are not covered:
publishing, countering, delegating, refreshing and forwarding
calendar components, as well as replacing the Organizer of a calendar
component. It is expected that future extensions will be developed
to address these.
This specification defines a client/server scheduling protocol, where
the server is made responsible for sending scheduling messages and
processing incoming scheduling messages. The client operations of
creating, modifying or deleting a calendar component in a calendar is
enough to trigger the server to deliver the necessary scheduling
messages to the appropriate calendar users. This approach is
sometimes referred to as "implicit scheduling".
This specification only addresses how scheduling occurs with users on
a single system (i.e., scheduling between CalDAV servers, or some
other calendaring and scheduling system, is not defined). However,
this specification is compatible with servers being able to send or
receive scheduling messages with "external" users (e.g., using the
iCalendar Message-Based Interoperability Protocol iMIP [RFC6047]).
Section 3 defines the automated "Scheduling Operations", that allow a
client to store iCalendar data on a CalDAV server, with the server
taking specific actions in response. One of three scheduling
operations can take place: "create", "modify" or "remove", based on
the HTTP method used for the request, and a comparison between any
existing and any new iCalendar data.
Section 4 defines how the server processes scheduling messages sent
as the result of a scheduling operation.
Section 5 defines how freebusy requests with an immediate response
are accomplished.
Section 6 defines access control privileges for the scheduling
operations defined in this specification.
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For the majority of the following discussion, scheduling of events
will be discussed. However, scheduling of to-dos is also fully
supported by this specification.
Discussion of this Internet-Draft is taking place on the mailing
lists at <https://www.ietf.org/mailman/listinfo/caldav> and
<http://lists.osafoundation.org/pipermail/ietf-caldav>.
1.1. Terminology
This specification reuses much of the same terminology as iCalendar
[RFC5545], iTIP [RFC5546], WebDAV [RFC4918], and CalDAV [RFC4791].
Additional terms used by this specification are:
Scheduling object resource: A calendar object resource contained in
a calendar collection for which the server will take care of
sending scheduling messages on behalf of the owner of the calendar
collection.
Organizer scheduling object resource: A scheduling object resource
owned by the Organizer.
Attendee scheduling object resource: A scheduling object resource
owned by an Attendee.
Scheduling operation: Add, change or remove operations on a
scheduling object resource for which the server will deliver
scheduling messages to other calendar users.
Scheduling message: A calendar object that describes a scheduling
operation such as schedule, reschedule, reply, or cancel.
Scheduling Outbox collection: A resource at which busy time
information requests are targeted.
Scheduling Inbox collection: A collection in which incoming
scheduling messages are delivered.
1.2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
The Augmented BNF (ABNF) syntax used by this document to specify the
format definition of new iCalendar elements is defined in [RFC5234].
The Augmented BNF (ABNF) syntax used by this document to specify the
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format definition of new message header fields to be used with the
HTTP/1.1 protocol is described in Section 2.1 of [RFC2616]. Since
this Augmented BNF uses the basic production rules provided in
Section 2.2 of [RFC2616], these rules apply to this document as well.
The term "protected" is used in the Conformance field of WebDAV
property definitions as defined in Section 15 of [RFC4918].
1.3. XML Namespaces and Processing
This document uses XML DTD fragments ([W3C.REC-xml-20081126], Section3.2) as a purely notational convention. WebDAV request and response
bodies cannot be validated by a DTD due to the specific extensibility
rules defined in Section 17 of [RFC4918] and due to the fact that all
XML elements defined by that specification use the XML namespace name
"DAV:". In particular:
1. element names use the "DAV:" namespace,
2. element ordering is irrelevant unless explicitly stated,
3. extension elements (elements not already defined as valid child
elements) can be added anywhere, except when explicitly stated
otherwise,
4. extension attributes (attributes not already defined as valid for
this element) can be added anywhere, except when explicitly
stated otherwise.
The XML elements specified in this document are defined in the
"urn:ietf:params:xml:ns:caldav" XML namespace registered by CalDAV
[RFC4791].
When XML element types in the namespaces "DAV:" and
"urn:ietf:params:xml:ns:caldav" are referenced in this document
outside of the context of an XML fragment, the strings "DAV:" and
"CALDAV:" will be prefixed to the element types, respectively.
This document inherits, and sometimes extends, DTD productions from
Section 14 of [RFC4918].
Also note that some CalDAV XML element names are identical to WebDAV
XML element names, though their namespace differs. Care needs to be
taken not to confuse the two sets of names.
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Internet-Draft CalDAV Scheduling Extensions April 20122. Scheduling Support
A server that supports the features described in this document is
REQUIRED to support the CalDAV "calendar-access" [RFC4791] feature.
Servers include "calendar-auto-schedule" as a field in the DAV
response header from an OPTIONS request on any resource that supports
any scheduling operations, properties, privileges or methods.
This specification introduces new collection resource types that are
used to manage scheduling object resources, and scheduling privileges
(as per Section 6), as well as provide scheduling functionality. It
is the server's responsibility to create these collection resources,
and clients have no way to create or delete them.
2.1. Scheduling Outbox Collection
A scheduling Outbox collection is used as the target for busy time
information requests, and to manage privileges that apply to outgoing
scheduling requests.
A scheduling Outbox collection MUST report the DAV:collection and
CALDAV:schedule-outbox XML elements in the value of the DAV:
resourcetype property. The element type declaration for CALDAV:
schedule-outbox is:
<!ELEMENT schedule-outbox EMPTY>
Example:
<D:resourcetype xmlns:D="DAV:">
<D:collection/>
<C:schedule-outbox xmlns:C="urn:ietf:params:xml:ns:caldav"/>
</D:resourcetype>
A scheduling Outbox collection MUST NOT be a child (at any depth) of
a calendar collection resource.
The following WebDAV properties specified in CalDAV "calendar-access"
[RFC4791] MAY also be defined on scheduling Outbox collections and
apply to scheduling messages submitted to the scheduling Outbox
collection with the POST method:
o CALDAV:supported-calendar-component-set
o CALDAV:supported-calendar-data
o CALDAV:max-resource-size
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o CALDAV:min-date-time
o CALDAV:max-date-time
o CALDAV:max-attendees-per-instance
The use of child resources in a scheduling Outbox collection is
reserved for future revisions or extensions of this specification.
The following WebDAV property is defined on principal resources and
used to locate the corresponding Outbox collection for the associated
principal.
2.1.1. CALDAV:schedule-outbox-URL Property
Name: schedule-outbox-URL
Namespace: urn:ietf:params:xml:ns:caldav
Purpose: Identify the URL of the scheduling Outbox collection owned
by the associated principal resource.
Protected: This property MAY be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: This property is needed for a client to determine where
the scheduling Outbox collection of the current user is located so
that sending of scheduling messages can occur. If not present,
then the associated calendar user is not enabled for the sending
of scheduling messages on the server.
Definition:
<!ELEMENT schedule-outbox-URL (DAV:href)>
2.2. Scheduling Inbox Collection
A scheduling Inbox collection contains copies of incoming scheduling
messages. These can be requests sent by an Organizer, or replies
sent by an Attendee in response to a request. The scheduling Inbox
collection is also used to manage scheduling privileges.
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The following WebDAV property is defined on principal resources and
used to locate the corresponding Inbox collection for the associated
principal.
2.2.1. CALDAV:schedule-inbox-URL Property
Name: schedule-inbox-URL
Namespace: urn:ietf:params:xml:ns:caldav
Purpose: Identify the URL of the scheduling Inbox collection owned
by the associated principal resource.
Protected: This property MAY be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: This property allows a client to determine where the
scheduling Inbox collection of the current user is located so that
processing of scheduling messages can occur. If not present, then
the associated calendar user is not enabled for reception of
scheduling messages on the server.
Definition:
<!ELEMENT schedule-inbox-URL (DAV:href)>
2.3. Calendaring Reports Extensions
This specification extends the CALDAV:calendar-query and CALDAV:
calendar-multiget REPORTs to return results for calendar object
resources in scheduling Inbox collections.
When a CALDAV:calendar-query REPORT includes a time-range query and
targets a scheduling Inbox collection, if any calendar object
resources contain "VEVENT" calendar components that do not include a
"DTSTART" iCalendar property (as allowed by iTIP [RFC5546]) then such
components MUST always match the time-range query test.
Note that the CALDAV:free-busy-query REPORT is not supported on
scheduling Inbox collections.
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Internet-Draft CalDAV Scheduling Extensions April 20122.4. Additional Principal Properties
This section defines new properties for WebDAV principal resources as
defined in [RFC3744]. These properties are likely to be protected
but the server MAY allow them to be written by appropriate users.
2.4.1. CALDAV:calendar-user-address-set Property
Name: calendar-user-address-set
Namespace: urn:ietf:params:xml:ns:caldav
Purpose: Identify the calendar addresses of the associated principal
resource.
Protected: This property MAY be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: Support for this property is REQUIRED. This property
is needed to map calendar user addresses in iCalendar data to
principal resources and their associated scheduling Inbox and
Outbox collections. In the event that a user has no well defined
identifier for their calendar user address, the URI of their
principal resource can be used. This property SHOULD be
searchable using the DAV:principal-property-search REPORT. The
DAV:principal-search-property-set REPORT SHOULD identify this
property as such. If not present, then the associated calendar
user is not enabled for scheduling on the server.
Definition:
<!ELEMENT calendar-user-address-set (DAV:href*)>
Example:
<C:calendar-user-address-set xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:href>mailto:bernard@example.com</D:href>
<D:href>mailto:bernard.desruisseaux@example.com</D:href>
</C:calendar-user-address-set>
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Internet-Draft CalDAV Scheduling Extensions April 20122.4.2. CALDAV:calendar-user-type Property
Name: calendar-user-type
Namespace: urn:ietf:params:xml:ns:caldav
Purpose: Identifies the calendar user type of the associated
principal resource.
Value: Same values allowed for the iCalendar "CUTYPE" property
parameter defined in Section 3.2.3 of [RFC5545].
Protected: This property MAY be protected.
PROPFIND behavior: This property SHOULD NOT be returned by a
PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value SHOULD be preserved in COPY
and MOVE operations.
Description: Clients can query principal resources in order to
lookup attendees available on the server. When doing this, it is
useful to know, or restrict the query to, certain types of
calendar user (e.g., only search for "people", or only search for
"rooms"). This property MAY be defined on principal resources to
indicate the type of calendar user associated with the principal
resource. Its value is the same as the iCalendar "CUTYPE"
property parameter that can be used on "ATTENDEE" properties.
This property SHOULD be searchable using the DAV:principal-
property-search REPORT. The DAV:principal-search-property-set
REPORT SHOULD identify this property as such.
Definition:
<!ELEMENT calendar-user-type (#PCDATA)>
Example:
<C:calendar-user-type
xmlns:C="urn:ietf:params:xml:ns:caldav">INDIVIDUAL<
/C:calendar-user-type>
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Internet-Draft CalDAV Scheduling Extensions April 20123. Scheduling Operations
When a calendar object resource is created, modified or removed from
a calendar collection, the server examines the calendar data and
checks to see whether the data represents a scheduling object
resource. If it does, the server will automatically attempt to
deliver a scheduling message to the appropriate calendar users.
Several types of scheduling operations can occur in this case,
equivalent to iTIP "REQUEST", "REPLY", "CANCEL", and "ADD"
operations.
3.1. Identifying Scheduling Object Resources
Calendar object resources on which the server performs scheduling
operations are referred to as scheduling object resources. There are
two types of scheduling object resources: organizer scheduling object
resources, and attendee scheduling object resources.
A calendar object resource is considered to be a valid organizer
scheduling object resource if the "ORGANIZER" iCalendar property is
present and set in all the calendar components to a value that
matches one of the calendar user addresses of the owner of the
calendar collection.
A calendar object resource is considered to be a valid attendee
scheduling object resource if the "ORGANIZER" iCalendar property is
present and set in all the calendar components to the same value and
doesn't match one of the calendar user addresses of the owner of the
calendar collection, and at least one of the "ATTENDEE" iCalendar
property values matches one of the calendar user addresses of the
owner of the calendar collection.
The creation of attendee scheduling object resources is typically
done by the server, with the resource being created in an appropriate
calendar collection (see Section 4.3).
3.2. Handling Scheduling Object Resources
The server's behavior when processing a scheduling object resource
depends on whether it is owned by the Organizer or an Attendee
specified in the calendar data.
3.2.1. Organizer Scheduling Object Resources
An Organizer can create, modify or remove a scheduling object
resource, subject to access privileges, pre-conditions, and the
restrictions defined in Section 4.1 of [RFC4791]. These operations
are each described next, and how they are invoked via HTTP requests
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is described in Section 3.2.3.
The Organizer of a calendar component can also be an Attendee of that
calendar component. In such cases the server MUST NOT send a
scheduling message to the Attendee that matches the Organizer.
The server SHOULD reject any attempt to set the "PARTSTAT" iCalendar
property parameter value of the "ATTENDEE" iCalendar property of
other users in the calendar object resource to a value other than
"NEEDS-ACTION" if the "SCHEDULE-AGENT" property parameter value is
not present or set to the value "SERVER".
The server MAY reject attempts to create a scheduling object resource
that specifies a "UID" property value already specified in a
scheduling object resource contained in another calendar collection
of the Organizer.
3.2.1.1. Create
When an Organizer creates a scheduling object resource, the server
MUST inspect each "ATTENDEE" property to determine whether to send a
scheduling message. The table below indicates the appropriate iTIP
method used by the server, taking into account any "SCHEDULE-AGENT"
property parameter (see Section 7.1) specified on each "ATTENDEE"
property.
+------------------+-------------+
| SCHEDULE-AGENT | iTIP METHOD |
+------------------+-------------+
| SERVER (default) | REQUEST |
| | |
| CLIENT | -- |
| | |
| NONE | -- |
+------------------+-------------+
"SCHEDULE-STATUS" iCalendar property parameters are added or changed
on "ATTENDEE" iCalendar properties in the scheduling object resource
being created as described in Section 7.3, with the value set as
described in Section 3.2.9. This will result in the created calendar
object resource differing from the calendar data sent in the HTTP
request. As a result clients MAY reload the calendar data from the
server in order to update to the new server generated state
information.
The server MUST add a "SCHEDULE-STATUS" iCalendar property parameter
(see Section 7.3) to the "ATTENDEE" iCalendar property in the
scheduling object resource being created, and set its value as
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described in Section 3.2.9. This will result in the created calendar
object resource differing from the calendar data sent in the HTTP
request. As a result clients MAY reload the calendar data from the
server in order to update to the new server generated state
information. Servers MUST NOT set the "SCHEDULE-STATUS" property
parameter on the "ATTENDEE" property of Attendees for which it did
not attempt to deliver a scheduling message.
The server MUST return an error with the CALDAV:allowed-organizer-
scheduling-object-change precondition code (Section 3.2.4.3) when the
Organizer attempts to change the iCalendar data in a manner that is
forbidden.
3.2.1.2. Modify
When an Organizer modifies a scheduling object resource, the server
MUST inspect each "ATTENDEE" property in both the original and
modified iCalendar data on a per-instance basis to determine whether
to send a scheduling message. The table below indicates the
appropriate iTIP method used by the server, taking into account any
"SCHEDULE-AGENT" property parameter (see Section 7.1) specified on
each "ATTENDEE" property. The values "SERVER", "CLIENT", and "NONE"
in the top and left titles of the table refer to the "SCHEDULE-AGENT"
parameter value of the "ATTENDEE" property, and the values "<Absent>"
and "<Removed>" are used to cover the cases where the "ATTENDEE"
property is not present (Original) or is being removed (Modified).
+---------------+-----------------------------------------------+
| | Modified |
| +-----------+-----------+-----------+-----------+
| | <Removed> | SERVER | CLIENT | NONE |
| | | (default) | | |
+===+===========+===========+===========+===========+===========+
| | <Absent> | -- | REQUEST / | -- | -- |
| O | | | ADD | | |
| r +-----------+-----------+-----------+-----------+-----------+
| i | SERVER | CANCEL | REQUEST | CANCEL | CANCEL |
| g | (default) | | | | |
| i +-----------+-----------+-----------+-----------+-----------+
| n | CLIENT | -- | REQUEST / | -- | -- |
| a | | | ADD | | |
| l +-----------+-----------+-----------+-----------+-----------+
| | NONE | -- | REQUEST / | -- | -- |
| | | | ADD | | |
+---+-----------+-----------+-----------+-----------+-----------+
"SCHEDULE-STATUS" iCalendar property parameters are added or changed
on "ATTENDEE" iCalendar properties in the scheduling object resource
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being modified as described in Section 7.3, with the value set as
described in Section 3.2.9. This will result in the created calendar
object resource differing from the calendar data sent in the HTTP
request. As a result clients MAY reload the calendar data from the
server in order to update to the new server generated state
information.
The server MUST return an error with the CALDAV:allowed-organizer-
scheduling-object-change precondition code (Section 3.2.4.3) when the
Organizer attempts to change the iCalendar data in a manner that is
forbidden.
3.2.1.3. Remove
When an Organizer removes a scheduling object resource, the server
MUST inspect each "ATTENDEE" property to determine whether to send a
scheduling message. The table below indicates the appropriate iTIP
method used by the server, taking into account any "SCHEDULE-AGENT"
property parameter (see Section 7.1) specified on each "ATTENDEE"
property.
+------------------+-------------+
| SCHEDULE-AGENT | iTIP METHOD |
+------------------+-------------+
| SERVER (default) | CANCEL |
| | |
| CLIENT | -- |
| | |
| NONE | -- |
+------------------+-------------+
3.2.2. Attendee Scheduling Object Resources
An Attendee can create, modify or remove a scheduling object
resource. These operations are each described next, and how they are
invoked via HTTP requests is described in Section 3.2.3.
3.2.2.1. Allowed Attendee Changes
Attendees are allowed to make some changes to a scheduling object
resource, though key properties such as start time, end time,
location, and summary are typically under the control of the
Organizer.
Servers MUST allow Attendees to make the following iCalendar data
changes, subject to other restrictions, such as access privileges and
pre-conditions:
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1. change their own "PARTSTAT" iCalendar property parameter value.
2. add, modify or remove any "TRANSP" iCalendar properties.
3. add, modify or remove any "PERCENT-COMPLETE" iCalendar
properties.
4. add, modify or remove any "COMPLETED" iCalendar properties.
5. add, modify or remove any "VALARM" iCalendar components.
6. add, modify or remove the "CALSCALE" iCalendar property within
the top-level "VCALENDAR" component.
7. modify the "PRODID" iCalendar property within the top-level
"VCALENDAR" component.
8. add "EXDATE" iCalendar properties and possibly remove components
for overridden recurrence instances.
9. add, modify or remove any "CREATED", "DTSTAMP" and "LAST-
MODIFIED" iCalendar properties.
10. add, modify or remove "SCHEDULE-STATUS" iCalendar property
parameters on "ATTENDEE" properties that have a "SCHEDULE-AGENT"
parameter set to "CLIENT".
11. add new components to represent overridden recurrence instances,
provided the only changes to the recurrence instance follow the
rules above.
The server MUST return an error with the CALDAV:allowed-attendee-
scheduling-object-change precondition code (Section 3.2.4.4) when the
Attendee attempts to change the iCalendar data in a manner forbidden
by the server.
3.2.2.2. Create
Typically an Attendee does not create scheduling object resources, as
scheduling messages delivered to them on the server are automatically
processed by the server and placed on one of their calendars (see
Section 4). However, in some cases a scheduling message can get
delivered directly to the client (e.g., via email [RFC6047]), and the
Attendee might wish to store that on the server. In that case the
client creates a scheduling object resource in a calendar belonging
to the Attendee. It can then set the "SCHEDULE-AGENT" iCalendar
property parameter on all "ORGANIZER" iCalendar properties in the
resource to determine how the server treats the resource. The value
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of the "SCHEDULE-AGENT" iCalendar property parameter on all
"ORGANIZER" iCalendar properties MUST be the same.
+----------------+--------------------------------------------------+
| SCHEDULE-AGENT | Action |
+----------------+--------------------------------------------------+
| SERVER | The server will attempt to process changes to |
| (default) | the resource using the normal rules for attendee |
| | scheduling object resources. |
| | |
| CLIENT | The server does no special processing of the |
| | resource. The client is assumed to be handling |
| | Attendee replies etc. |
| | |
| NONE | The server does no special processing of the |
| | resource. |
+----------------+--------------------------------------------------+
"SCHEDULE-STATUS" iCalendar property parameters are added or changed
on "ORGANIZER" iCalendar properties in the scheduling object resource
being created as described in Section 7.3, with the value set as
described in Section 3.2.9.
3.2.2.3. Modify
When a scheduling object resource is modified by an Attendee, the
server behavior depends on the value of the "SCHEDULE-AGENT"
iCalendar property parameter on the "ORGANIZER" iCalendar properties:
+----------------+--------------------------------------------------+
| SCHEDULE-AGENT | Action |
+----------------+--------------------------------------------------+
| SERVER | The server will attempt to process the update |
| (default) | using the behavior listed below. |
| | |
| CLIENT | The server does no special processing of the |
| | resource. The client is assumed to be handling |
| | any Attendee replies etc. |
| | |
| NONE | The server does no special processing of the |
| | resource. |
+----------------+--------------------------------------------------+
The server will inspect the changes by comparing the new scheduling
object resource with the existing scheduling object resource.
If the Attendee changes one or more "PARTSTAT" iCalendar property
values on any component, or adds an overridden component with a
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changed "PARTSTAT" property, then the server MUST deliver an iTIP
"REPLY" scheduling message to the Organizer to indicate the new
participation status of the Attendee.
If the Attendee adds an "EXDATE" property value to effectively remove
a recurrence instance, the server MUST deliver an iTIP "REPLY"
scheduling message to the Organizer to indicate that the Attendee has
declined the instance.
"SCHEDULE-STATUS" iCalendar property parameters are added or changed
on "ORGANIZER" iCalendar properties in the scheduling object resource
being modified as described in Section 7.3, with the value set as
described in Section 3.2.9. This will result in the updated calendar
object resource differing from the calendar data sent in the HTTP
request. As a result clients MAY reload the calendar data from the
server in order to update to the new server generated state
information.
3.2.2.4. Remove
When a scheduling object resource is removed by an Attendee, the
server behavior depends on the value of the "SCHEDULE-AGENT"
iCalendar property parameter on the "ORGANIZER" iCalendar properties:
+----------------+--------------------------------------------------+
| SCHEDULE-AGENT | Action |
+----------------+--------------------------------------------------+
| SERVER | The server will attempt to process the removal |
| (default) | taking into account any "Schedule-Reply" request |
| | header as per Section 8.1. |
| | |
| CLIENT | The server does no special processing of the |
| | resource. The client is assumed to be handling |
| | any Attendee replies etc. |
| | |
| NONE | The server does no special processing of the |
| | resource. |
+----------------+--------------------------------------------------+
3.2.3. HTTP Methods
This section describes how use of various HTTP [RFC2616] and WebDAV
[RFC4918] methods on a scheduling object resource will cause a
create, modify or remove operation on that resource as described
above. The use of these methods is subject to the restrictions in
[RFC4791], in addition to what is described below.
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Definition:
<!ELEMENT allowed-attendee-scheduling-object-change EMPTY>
3.2.5. DTSTAMP and SEQUENCE Properties
The server MUST ensure that a "DTSTAMP" iCalendar property is present
and set the value to the UTC time that the scheduling message was
generated (as required by iCalendar).
The server MUST ensure that for each type of scheduling operation,
the "SEQUENCE" iCalendar property value is updated as per iTIP
[RFC5546].
3.2.6. Restrict Recurrence Instances Sent to Attendees
Servers MUST ensure that Attendees only get information about
recurrence instances that explicitly include them as an Attendee,
when delivering scheduling messages for recurring calendar
components.
For example, if an Attendee is invited to only a single instance of a
recurring event, the organizer scheduling object resource will
contain an overridden instance in the form of a separate calendar
component. That separate calendar component will include the
"ATTENDEE" property referencing the "one-off" Attendee. That
Attendee will not be listed in any other calendar components in the
scheduling object resource. Any scheduling messages delivered to the
Attendee will only contain information about this overridden
instance.
As another example, an Attendee could be excluded from one instance
of a recurring event. In that case the organizer scheduling object
resource will include an overridden instance with an "ATTENDEE" list
that does not include the Attendee being excluded. Any scheduling
messages delivered to the Attendee will not specify the overridden
instance but rather include an "EXDATE" property in the "master"
component that defines the recurrence set.
3.2.7. Forcing the Server to Send a Scheduling Message
The iCalendar property parameter "SCHEDULE-FORCE-SEND" defined in
Section 7.2 can be used by a calendar user to force the server to
send a scheduling message to an Attendee or the Organizer in a
situation where the server would not normally send a scheduling
message. For instance, an Organizer could use this property
parameter to request an Attendee, that previously declined an
invitation, to reconsider their participation status without being
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forced to modify the event.
3.2.8. Attendee Participation Status
This section specifies additional requirements on the handling of the
"PARTSTAT" property parameter when the "SCHEDULE-AGENT" property
parameter on the corresponding "ATTENDEE" property is set to the
value "SERVER" or is not present.
A reschedule occurs when any "DTSTART", "DTEND", "DURATION", "DUE",
"RRULE", "RDATE", or "EXDATE" property changes in a calendar
component such that existing recurrence instances are impacted by the
changes, as shown in the table below. Servers MUST reset the
"PARTSTAT" property parameter value of all "ATTENDEE" properties,
except the one that corresponds to the Organizer, to "NEEDS-ACTION"
for each calendar component change that causes any instance to be
rescheduled.
+-----------+-------------------------------------------------------+
| Property | Server Action |
+-----------+-------------------------------------------------------+
| DTSTART, | Any change to these properties result in "PARTSTAT" |
| DTEND, | being set to "NEEDS-ACTION" |
| DURATION, | |
| DUE | |
| | |
| | |
| | |
| RRULE | A change to or addition of this property that results |
| | in the addition of new recurring instances or a |
| | change in time for existing recurring instances |
| | result in "PARTSTAT" being reset to "NEEDS-ACTION" on |
| | each affected component. |
| | |
| | |
| | |
| RDATE | A change to or addition of this property that results |
| | in the addition of new recurring instances or a |
| | change in time for existing recurring instances |
| | result in "PARTSTAT" being reset to "NEEDS-ACTION" on |
| | each affected component. |
| | |
| | |
| | |
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| EXDATE | A change to or removal of this property that results |
| | in the re-instatement of recurring instances result |
| | in "PARTSTAT" being set to "NEEDS-ACTION" on each |
| | affected component. |
+-----------+-------------------------------------------------------+
The server MAY allow the Organizer's client to change an Attendee's
"PARTSTAT" property parameter value to "NEEDS-ACTION" at any other
time (e.g., when the "LOCATION" property value changes, an Organizer
might wish to re-invite Attendees who might be impacted by the
change).
3.2.9. Schedule Status Values
When scheduling with an Attendee there are two types of status
information that can be returned during the operation. The first
type of status information is a "delivery" status that indicates
whether the scheduling message from the Organizer to the Attendee was
delivered or not, or what the current status of delivery is. The
second type of status information is a "reply" status corresponding
to the Attendee's own "REQUEST-STATUS" information from the
scheduling message reply that is sent back to the Organizer.
Similarly, when an Attendee sends a reply back to the Organizer,
there will be "delivery" status information for the scheduling
message sent to the Organizer. However, there is no "REQUEST-STATUS"
sent back by the Organizer, so there is no equivalent of the "reply"
status as per scheduling messages to Attendees.
The "delivery" status information on an "ORGANIZER" or "ATTENDEE"
iCalendar property is conveyed in the "SCHEDULE-STATUS" property
parameter value (Section 7.3). The status code value for "delivery"
status can be one of the following:
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| 5.2 | The scheduling message was not delivered because the |
| | server was not able to find a way to deliver the |
| | message. This is likely a permanent failure, and the |
| | originator ought not try to send the message again, at |
| | least without verifying/correcting the calendar user |
| | address of the recipient. |
| | |
| | |
| | |
| 5.3 | The scheduling message was not delivered and was |
| | rejected because scheduling with that recipient is not |
| | allowed. This is likely a permanent failure, and the |
| | originator ought not try to send the message again. |
+----------+--------------------------------------------------------+
The status code for "reply" status can be any of the valid iTIP
[RFC5546] "REQUEST-STATUS" values.
The 1.xx "REQUEST-STATUS" codes are new. This specification modifies
item (2) of Section 3.6 of [RFC5546] by adding the following
restriction:
For a 1.xx code, all components MUST have exactly the same code.
Definition of the new 1.xx codes is as follows:
3.2.9.1. Status Code 1.0
Status Code: 1.0
Status Description: Pending.
Status Exception Data: None.
Description: Delivery of the iTIP message is pending.
3.2.9.2. Status Code 1.1
Status Code: 1.1
Status Description: Sent.
Status Exception Data: None.
Description: The iTIP message has been sent, though no information
about successful delivery is known.
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Internet-Draft CalDAV Scheduling Extensions April 20123.2.9.3. Status Code 1.2
Status Code: 1.2
Status Description: Delivered.
Status Exception Data: None.
Description: The iTIP message has been sent and delivered.
3.2.10. Avoiding Conflicts when Updating Scheduling Object Resources
Scheduling object resources on the server might change frequently as
Attendees change their participation status, triggering updates to
the Organizer, and refreshes of other Attendees' copies of the
scheduling object resource. This can lead to an "inconsequential"
change to a calendar user's data - one that does not directly impact
their own participation status. When this occurs, clients have to
reload calendar data and reconcile with changes being made by
calendar users. To avoid the need for this, the server can instead
merge calendar data changes from a client with changes made as a the
result of a scheduling operation carried out by some other calendar
user.
This specification introduces a new WebDAV resource property CALDAV:
schedule-tag with a corresponding response header "Schedule-Tag", and
a new "If-Schedule-Tag-Match" request header to allow client changes
to be appropriately merged with server changes in the case where the
changes on the server were the result of an "inconsequential"
scheduling message update (one which simply updates the status
information of Attendees due to a reply from another Attendee).
Servers MUST automatically resolve conflicts with "inconsequential"
changes done to scheduling object resources when the "If-Schedule-
Tag-Match" request header is specified. The If-Schedule-Tag-Match
request header applies only to the Request-URI, and not to the
Destination of a COPY or MOVE.
A response to any successful GET or PUT request targeting a
scheduling object resource MUST include a Schedule-Tag response
header with the value set to the same value as the CALDAV:schedule-
tag WebDAV property of the resource.
A response to any successful COPY or MOVE request that specifies a
Destination request header targeting a scheduling object resource
MUST include a Schedule-Tag response header with the value set to the
same value as the CALDAV:schedule-tag WebDAV property of the
destination resource.
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Clients SHOULD use the If-Schedule-Tag-Match header on requests that
update scheduling object resources, instead of HTTP ETag-based
precondition tests (e.g., If-Match). Normal ETag-based precondition
tests are used in all other cases, e.g., for synchronization.
The value of the CALDAV:schedule-tag property changes according to
these rules:
o For an Organizer's copy of a scheduling object resource:
1. The server MUST NOT change the CALDAV:schedule-tag property
value when the scheduling object resource is updated as the
result of automatically processing a scheduling message reply
from an Attendee. For instance, when an Attendee replies to
the Organizer, the CALDAV:schedule-tag property is unchanged
after the Organizer's scheduling object resource has been
automatically updated by the server with the Attendee's new
participation status.
2. The server MUST change CALDAV:schedule-tag property value when
the scheduling object resource is changed directly via an HTTP
request (e.g., PUT, COPY or MOVE).
o For an Attendee's copy of a scheduling object resource:
1. The server MUST change the CALDAV:schedule-tag property value
when the scheduling object resource is changed as the result
of processing a scheduling message update from an Organizer
that contains changes other than just the participation status
of Attendees.
2. The server MUST NOT change the CALDAV:schedule-tag property
value when the scheduling object resource is changed as the
result of processing a scheduling message update from an
Organizer that only specify changes in the participation
status of Attendees. For instance, when Attendee "A" replies
to Organizer "O", and Attendee "B" receives a scheduling
message update from Organizer "O" with the new participation
status of Attendee "A", the CALDAV:schedule-tag property of
Attendee "B"s scheduling object resource would remain the
same.
3. The server MUST change the CALDAV:schedule-tag property value
when the scheduling object resource is changed directly via an
HTTP request (e.g., PUT, COPY or MOVE).
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Internet-Draft CalDAV Scheduling Extensions April 20123.2.10.1. PUT
Clients MAY use the If-Schedule-Tag-Match request header to do a PUT
request that ensures that "inconsequential" changes on the server do
not result in a precondition error. The value of the request header
is set to the last Schedule-Tag value received for the resource being
modified. If the value of the If-Schedule-Tag-Match header matches
the current value of the CALDAV:schedule-tag property the server MUST
take any "ATTENDEE" property changes for all Attendees other than the
owner of the scheduling object resource and apply those to the new
resource being stored. Otherwise, the server MUST fail the request
with a 412 Precondition Failed status code.
3.2.10.2. DELETE, COPY or MOVE
Clients MAY use the If-Schedule-Tag-Match request header to do a
DELETE, COPY or MOVE request that ensures that "inconsequential"
changes on the server do not result in a precondition error. The
value of the request header is set to the last Schedule-Tag value
received for the resource being deleted. If the value of the If-
Schedule-Tag-Match header matches the current value of the CALDAV:
schedule-tag property the server performs the normal DELETE, COPY or
MOVE request processing for the resource. Otherwise, the server MUST
fail the request with a 412 Precondition Failed status code.
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Internet-Draft CalDAV Scheduling Extensions April 20124. Processing Incoming Scheduling Messages
Scheduling operations can cause the delivery of a scheduling message
into an Organizer's or Attendee's scheduling Inbox collection.
Servers MUST automatically process incoming scheduling messages using
the rules defined by [RFC5546], by creating or updating the
corresponding scheduling object resources on calendars owned by the
owner of the scheduling Inbox collection. In addition, the
scheduling message is stored in the scheduling Inbox collection as an
indicator to the client that a scheduling operation has taken place.
Scheduling messages are typically removed from the scheduling Inbox
collection by the client once the calendar user has acknowledged the
change.
The server MUST take into account privileges on the scheduling Inbox
collection when processing incoming scheduling messages, to determine
whether delivery of the scheduling message is allowed. Privileges on
calendars containing any matching scheduling object resource are not
considered in this case (i.e., a schedule message from another user
can cause modifications to resources in calendar collections that the
other user would not normally have read or write access to).
Additionally, servers MUST take into account any scheduling Inbox
collection preconditions (see Section 2.2) when delivering the
scheduling message, and it MUST take into account the similar
preconditions on any calendar collection which contains, or would
contain, the corresponding scheduling object resource.
4.1. Processing Organizer Requests, Additions, and Cancellations
For a scheduling message sent by an Organizer, the server first tries
to locate a corresponding scheduling object resource belonging to the
Attendee. If no matching scheduling object resource exists, the
server treats the scheduling message as a new message, otherwise it
is treated as an update.
In the case of a new message, the server processes the scheduling
message and creates a new scheduling object resource as per
Section 4.3.
In the case of an update, the server processes the scheduling message
and updates the matching scheduling object resource belonging to the
Attendee to reflect the changes sent by the Organizer.
In each case, the scheduling message MUST only appear in the
Attendee's scheduling Inbox collection once all automatic processing
has been done.
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Internet-Draft CalDAV Scheduling Extensions April 20124.2. Processing Attendee Replies
For a scheduling message reply sent by an Attendee, the server first
locates the corresponding scheduling object resource belonging to the
Organizer. If the corresponding scheduling object resource cannot be
found, the server SHOULD ignore the scheduling message.
The server MUST then update the "PARTSTAT" iCalendar property
parameter value of each "ATTENDEE" iCalendar property in the
scheduling object resource to match the changes indicated in the
reply (taking into account the fact that an Attendee could have
created a new overridden iCalendar component to indicate different
participation status on one or more instances of a recurring event).
The server MUST also update or add the "SCHEDULE-STATUS" property
parameter on each matching "ATTENDEE" iCalendar property and set its
value to that of the "REQUEST-STATUS" property in the reply, or to
"2.0" if "REQUEST-STATUS" is not present (also taking into account
recurrence instances). If there are multiple "REQUEST-STATUS"
properties in the reply, the "SCHEDULE-STATUS" property parameter
value is set to a comma-separated list of status codes, one from each
"REQUEST-STATUS" property.
The server SHOULD send scheduling messages to all the other Attendees
indicating the change in participation status of the Attendee
replying, subject to the recurrence requirements of Section 3.2.6.
The scheduling message MUST only appear in the Organizer's scheduling
Inbox collection once all automatic processing has been done.
4.3. Default Calendar Collection
The server processes scheduling messages received for an Attendee by
creating a new scheduling object resource in a calendar collection
belonging to the Attendee, when one does not already exist. A
calendar user that is an Attendee in a scheduling operation MUST have
at least one valid calendar collection available. If there is no
valid calendar collection, then the server MUST reject the attempt to
deliver the scheduling message to the Attendee.
Servers MAY provide support for a default calendar collection, that
is, the calendar collection in which new scheduling object resources
will be created. The CALDAV:schedule-default-calendar-URL WebDAV
property, which can be present on the scheduling Inbox collection of
a calendar user, specifies if this calendar user has a default
calendar collection. See Section 9.2.
Servers SHOULD create new scheduling object resources in the default
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calendar collection, if the CALDAV:schedule-default-calendar-URL
WebDAV property is set.
Servers MAY allow clients to change the default calendar collection
by changing the value of the CALDAV:schedule-default-calendar-URL
WebDAV property on the scheduling Inbox collection. However, the
server MUST ensure that any new value for that property refers to a
valid calendar collection belonging to the owner of the scheduling
Inbox collection.
Servers MUST reject any attempt to delete the default calendar
collection.
4.3.1. Additional Method Preconditions
This specification defines additional method preconditions (see
Section 16 of WebDAV [RFC4918]) to provide machine-parseable
information in error responses.
4.3.1.1. CALDAV:default-calendar-needed Precondition
Name: default-calendar-needed
Namespace: urn:ietf:params:xml:ns:caldav
Apply to: DELETE
Use with: 403 Forbidden
Purpose: (precondition) -- The client attempted to delete the
calendar collection currently referenced by the CALDAV:schedule-
default-calendar-URL property, or attempted to remove the CALDAV:
schedule-default-calendar-URL property on the scheduling Inbox
collection on a server that doesn't allow such operations.
Definition:
<!ELEMENT default-calendar-needed EMPTY>
4.3.1.2. CALDAV:valid-schedule-default-calendar-URL Precondition
Name: valid-schedule-default-calendar-URL
Namespace: urn:ietf:params:xml:ns:caldav
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Internet-Draft CalDAV Scheduling Extensions April 20125. Request for Busy Time Information
Busy time information of one or more calendar users can be determined
by submitting a POST request targeted at the scheduling Outbox
collection of the calendar user requesting the information (the
Organizer). To accomplish this, the request body MUST contain a
"VFREEBUSY" calendar component with the "METHOD" iCalendar property
set to the value "REQUEST" as specified in Section 3.3.2 of iTIP
[RFC5546]. The resource identified by the Request-URI MUST be a
resource collection of type CALDAV:schedule-outbox (Section 2.1).
The "ORGANIZER" property value in the "VFREEBUSY" component MUST
match one of the calendar user addresses of the owner of the Outbox
collection.
A response to a busy time request that indicates status for one or
more calendar users MUST be an XML document with a CALDAV:schedule-
response XML element as its root element. This element MUST contain
one CALDAV:response element for each calendar user, with each of
those containing elements that indicate which calendar user they
correspond to, the scheduling status for that calendar user, any
error codes and an optional description. For a successful busy time
request, a CALDAV:calendar-data element is also present for each
calendar user, containing the actual busy time information (i.e., an
iCalendar "VFREEBUSY" component). See Section 10.1 for the detail on
the child elements. See Appendix B.5 for an example busy time
request and response.
5.1. Status Codes
The list below summarizes the most common status codes used for this
method. However, clients need to be prepared to handle other 2/3/4/
5xx series status codes as well.
200 (OK) - The command succeeded.
204 (No Content) - The command succeeded.
400 (Bad Request) - The client has provided an invalid scheduling
message.
403 (Forbidden) - The client cannot submit a scheduling message to
the specified Request-URI.
404 (Not Found) - The URL in the Request-URI was not present.
423 (Locked) - The specified resource is locked and the client
either is not a lock owner or the lock type requires a lock token
to be submitted and the client did not submit it.
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Internet-Draft CalDAV Scheduling Extensions April 20126. Scheduling Privileges
New scheduling privileges are defined in this section. All the
scheduling privileges MUST be non-abstract and MUST appear in the
DAV:supported-privilege-set property of scheduling Outbox and Inbox
collections on which they are defined.
The tables specified in Appendix A clarify which scheduling methods
(e.g., "REQUEST", "REPLY", etc.) are controlled by each scheduling
privilege defined in this section.
6.1. Privileges on Scheduling Inbox Collections
This section defines new WebDAV ACL [RFC3744] privileges that are for
use on scheduling Inbox collections. These privileges determine
whether delivery of scheduling messages from a calendar user is
allowed by the calendar user who "owns" the scheduling Inbox
collection. This allows calendar users to choose which other
calendar users can schedule with them.
Note that when a scheduling message is delivered to a calendar user,
in addition to a scheduling object resource being created in the
calendar user's scheduling Inbox collection, a new scheduling object
resource might be created or an existing one updated in a calendar
belonging to the calendar user. In that case, the ability to create
or update the scheduling object resource in the calendar is
controlled by the privileges assigned to the scheduling Inbox
collection.
The privileges defined in this section are ignored if applied to a
resource other than a scheduling Inbox collection.
6.1.1. CALDAV:schedule-deliver Privilege
CALDAV:schedule-deliver is an aggregate privilege as per Section 6.3.
<!ELEMENT schedule-deliver EMPTY>
6.1.2. CALDAV:schedule-deliver-invite Privilege
The CALDAV:schedule-deliver-invite privilege controls the processing
and delivery of scheduling messages coming from an Organizer.
<!ELEMENT schedule-deliver-invite EMPTY>
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Internet-Draft CalDAV Scheduling Extensions April 20126.1.3. CALDAV:schedule-deliver-reply Privilege
The CALDAV:schedule-deliver-reply privilege controls the processing
and delivery of scheduling messages coming from an Attendee.
<!ELEMENT schedule-deliver-reply EMPTY>
6.1.4. CALDAV:schedule-query-freebusy Privilege
The CALDAV:schedule-query-freebusy privilege controls freebusy
requests targeted at the owner of the scheduling Inbox collection.
<!ELEMENT schedule-query-freebusy EMPTY>
6.2. Privileges on Scheduling Outbox Collections
This section defines new WebDAV ACL [RFC3744] privileges that are
defined for use on scheduling Outbox collections. These privileges
determine which calendar users are allowed to send scheduling
messages on behalf of the calendar user who "owns" the scheduling
Outbox collection. This allows calendar users to choose other
calendar users who can act on their behalf (e.g. assistants working
on behalf of their boss).
The privileges defined in this section are ignored if applied to a
resource other than a scheduling Outbox collection.
6.2.1. CALDAV:schedule-send Privilege
CALDAV:schedule-send is an aggregate privilege as per Section 6.3.
<!ELEMENT schedule-send EMPTY>
6.2.2. CALDAV:schedule-send-invite Privilege
The CALDAV:schedule-send-invite privilege controls the sending of
scheduling messages by Organizers.
Users granted the DAV:bind privilege on a calendar collection, or
DAV:write privilege on scheduling object resources, will also need
the CALDAV:schedule-send-invite privilege granted on the scheduling
Outbox collection of the owner of the calendar collection or
scheduling object resource in order to be allowed to create, modify
or delete scheduling object resources in a way that will trigger the
CalDAV server to deliver scheduling messages to attendees.
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<!ELEMENT schedule-send-invite EMPTY>
6.2.3. CALDAV:schedule-send-reply Privilege
The CALDAV:schedule-send-reply privilege controls the sending of
scheduling messages by Attendees.
Users granted the DAV:bind privilege on a calendar collection, or
DAV:write privilege on scheduling object resources, will also need
the CALDAV:schedule-send-reply privilege granted on the scheduling
Outbox collection of the owner of the calendar collection or
scheduling object resource in order to be allowed to create, modify
or delete scheduling object resources in a way that will trigger the
CalDAV server to deliver scheduling message replies to the organizer.
<!ELEMENT schedule-send-reply EMPTY>
6.2.4. CALDAV:schedule-send-freebusy Privilege
The CALDAV:schedule-send-freebusy privilege controls the use of the
POST method to submit scheduling messages that specify the scheduling
method "REQUEST" with a "VFREEBUSY" calendar component.
<!ELEMENT schedule-send-freebusy EMPTY>
6.3. Aggregation of Scheduling Privileges
Server implementations MUST aggregate the scheduling privileges as
follows:
DAV:all contains CALDAV:schedule-send and CALDAV:schedule-deliver;
CALDAV:schedule-send contains CALDAV:schedule-send-invite, CALDAV:
schedule-send-reply, and CALDAV:schedule-send-freebusy;
CALDAV:schedule-deliver contains CALDAV:schedule-deliver-invite,
CALDAV:schedule-deliver-reply, and CALDAV:schedule-query-freebusy.
The following diagram illustrates how scheduling privileges are
aggregated according to the above requirements.
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Internet-Draft CalDAV Scheduling Extensions April 20127. Additional iCalendar Property Parameters
This specification defines additional iCalendar property parameters
to support the CalDAV scheduling extensions.
7.1. Schedule Agent Parameter
Parameter Name: SCHEDULE-AGENT
Purpose: To specify the agent expected to deliver scheduling
messages to the corresponding Organizer or Attendee.
Format Definition: This property parameter is defined by the
following notation:
scheduleagentparam = "SCHEDULE-AGENT" "="
("SERVER" ; The server handles scheduling
/ "CLIENT" ; The client handles scheduling
/ "NONE" ; No scheduling
/ x-name ; Experimental type
/ iana-token) ; Other IANA registered type
;
; If the parameter is not present its value defaults to SERVER.
; "x-name" and "iana-token" are defined in Section 3.1 of
; [RFC5545].
Description: This property parameter MAY be specified on "ORGANIZER"
or "ATTENDEE" iCalendar properties. In the absence of this
parameter, the value "SERVER" MUST be used for the default
behavior. The value determines whether or not a scheduling
operation on a server will cause a scheduling message to be sent
to the corresponding calendar user identified by the "ORGANIZER"
or "ATTENDEE" property value. When the value "SERVER" is
specified, or the parameter is absent, then it is the server's
responsibility to send a scheduling message as part of a
scheduling operation. When the value "CLIENT" is specified, that
indicates that the client is handling scheduling messages with the
calendar user itself. When "NONE" is specified, no scheduling
messages are being sent to the calendar user.
Servers MUST NOT include this parameter in any scheduling messages
sent as the result of a scheduling operation.
Clients MUST NOT include this parameter in any scheduling messages
that they themselves send.
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The parameter value MUST be the same on every "ORGANIZER" property
in a scheduling object resource.
The parameter value MUST be the same on each "ATTENDEE" property
whose values match in a scheduling object resource.
Servers and clients MUST treat x-name and iana-token values they
do not recognize the same way as they would the "NONE" value.
Example:
ORGANIZER;SCHEDULE-AGENT=SERVER:mailto:bernard@example.com
ATTENDEE;SCHEDULE-AGENT=NONE:mailto:cyrus@example.com
7.2. Schedule Force Send Parameter
Parameter Name: SCHEDULE-FORCE-SEND
Purpose: To force a scheduling message to be sent to the calendar
user specified by the property.
Format Definition: This property parameter is defined by the
following notation:
scheduleforcesendparam = "SCHEDULE-FORCE-SEND" "="
("REQUEST" ; Force a "REQUEST"
/ "REPLY" ; Force a "REPLY"
/ iana-token)
;
; "iana-token" is defined in Section 3.1 of [RFC5545]. Its value
; MUST be an IANA registered iCalendar "METHOD" property value.
Description: This property parameter MAY be specified on "ATTENDEE"
and "ORGANIZER" properties on which the "SCHEDULE-AGENT" property
parameter is set to the value "SERVER" or is not specified. This
property parameter is used to force a server to send a scheduling
message to a specific calendar user in situations where the server
would not send a scheduling message otherwise (e.g., when no
change that warrants the delivery of a new scheduling message was
performed on the scheduling object resource). An Organizer MAY
specify this parameter on an "ATTENDEE" property with the value
"REQUEST" to force a "REQUEST" scheduling message to be sent to
this Attendee. An Attendee MAY specify this parameter on the
"ORGANIZER" with the value "REPLY" to force a "REPLY" scheduling
message to be sent to the Organizer.
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Servers MUST NOT preserve this property parameter in scheduling
object resources, nor include it in any scheduling messages sent
as the result of a scheduling operation.
Clients MUST NOT include this parameter in any scheduling messages
that they themselves send.
Servers MUST set the "SCHEDULE-STATUS" parameter of the "ATTENDEE"
or "ORGANIZER" to 2.3 (i.e., "Success, invalid property parameter
ignored", see Section 3.6 of [RFC5546]) when the "SCHEDULE-FORCE-
SEND" parameter is set to an iana-token value they do not
recognize.
Example:
ORGANIZER;SCHEDULE-FORCE-SEND=REPLY:mailto:cyrus@example.com
ATTENDEE;SCHEDULE-FORCE-SEND=REQUEST:mailto:bernard@example.com
7.3. Schedule Status Parameter
Parameter Name: SCHEDULE-STATUS
Purpose: To specify the status codes returned from processing of the
most recent scheduling message sent to the corresponding Attendee,
or received from the corresponding Organizer.
Format Definition: This property parameter is defined by the
following notation:
schedulestatusparam = "SCHEDULE-STATUS" "="
( statcode
/ DQUOTE statcode *("," statcode) DQUOTE)
;
; "statcode" is defined in Section 3.8.8.3 of [RFC5545]. Value
; is a single "statcode" or a comma-separated list of "statcode"
; values.
Description: This property parameter MAY be specified on the
"ATTENDEE" and "ORGANIZER" properties.
Servers MUST only add or change this property parameter on any
"ATTENDEE" properties corresponding to calendar users who were
sent a scheduling message via a scheduling operation. Clients
SHOULD NOT change or remove this parameter if it was provided by
the server. In the case where the client is handling the
scheduling, the client MAY add, change or remove this parameter to
indicate the last scheduling message status it received.
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Servers MUST add this parameter to any "ORGANIZER" properties
corresponding to calendar users who were sent a scheduling message
reply by an Attendee via a scheduling operation. Clients SHOULD
NOT change or remove this parameter if it was provided by the
server. In the case where the client is handling the scheduling,
the client MAY add, change or remove this parameter to indicate
the last scheduling message status it received.
Servers MUST NOT include this parameter in any scheduling messages
sent as the result of a scheduling operation.
Clients MUST NOT include this parameter in any scheduling messages
that they themselves send.
Values for this property parameter are described in Section 3.2.9.
Example:
ATTENDEE;SCHEDULE-STATUS="2.0":mailto:bernard@example.com
ATTENDEE;SCHEDULE-STATUS="2.0,2.4":mailto:cyrus@example.com
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Internet-Draft CalDAV Scheduling Extensions April 20128. Additional Message Header Fields
This specification defines additional HTTP request and response
headers for use with CalDAV.
8.1. Schedule-Reply Request Header
Schedule-Reply = "Schedule-Reply" ":" ("T" | "F")
Example:
Schedule-Reply: F
When an Attendee removes a scheduling object resource as per
Section 3.2.2.4, and the Schedule-Reply header is not present, or
present and set to the value "T" (true), the server MUST send an
appropriate reply scheduling message with the Attendee's "PARTSTAT"
iCalendar property parameter value set to "DECLINED" as part of its
normal scheduling operation processing.
When the Schedule-Reply header is set to the value "F" (false), the
server MUST NOT send a scheduling message as part of its normal
scheduling operation processing.
The Schedule-Reply request header is used by a client to indicate to
a server whether or not a scheduling operation ought to occur when an
Attendee deletes a scheduling object resource. In particular it
controls whether a reply scheduling message is sent to the Organizer
as a result of the removal. There are situations in which
unsolicited scheduling messages need to be silently removed (or
ignored) for security or privacy reasons. This request header allows
the scheduling object resource to be removed if such a need arises.
8.2. Schedule-Tag Response Header
The Schedule-Tag response header provides the current value of the
CALDAV:schedule-tag property value. The behavior of this response
header is described in Section 3.2.10.
All scheduling object resources MUST support the Schedule-Tag header.
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Example:
Schedule-Tag: "12ab34-cd56ef"
8.3. If-Schedule-Tag-Match Request Header
The If-Schedule-Tag-Match request header field is used with a method
to make it conditional. Clients can set this header to the value
returned in the Schedule-Tag response header, or the CALDAV:schedule-
tag property, of a scheduling object resource previously retrieved
from the server to avoid overwriting "consequential" changes to the
scheduling object resource.
All scheduling object resources MUST support the If-Schedule-Tag-
Match header.
If-Schedule-Tag-Match = "If-Schedule-Tag-Match" ":" opaque-tag
; "opaque-tag" is defined in Section 3.11 of [RFC2616]
Example:
If-Schedule-Tag-Match: "12ab34-cd56ef"
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Internet-Draft CalDAV Scheduling Extensions April 20129. Additional WebDAV Properties
This specification defines the following new WebDAV properties for
use with CalDAV.
9.1. CALDAV:schedule-calendar-transp Property
Name: schedule-calendar-transp
Namespace: urn:ietf:params:xml:ns:caldav
Purpose: Determines whether the calendar object resources in a
calendar collection will affect the owner's busy time information.
Protected: This property MAY be protected and SHOULD NOT be returned
by a PROPFIND allprop request (as defined in Section 14.2 of
[RFC4918]).
COPY/MOVE behavior: This property value SHOULD be kept during a MOVE
operation, and SHOULD be copied and preserved in a COPY.
Description: This property SHOULD be defined on all calendar
collections. If present, it contains one of two XML elements that
indicate whether the calendar object resources in the calendar
collection ought to contribute to the owner's busy time. When the
CALDAV:opaque element is used, all calendar object resources in
the corresponding calendar collection MUST contribute to busy
time, assuming access privileges and other iCalendar properties
allow it to. When the CALDAV:transparent XML element is used, the
calendar object resources in the corresponding calendar collection
MUST NOT contribute to busy time.
If this property is not present on a calendar collection, then the
default value CALDAV:opaque MUST be assumed.
Definition:
<!ELEMENT schedule-calendar-transp (opaque | transparent)>
<!ELEMENT opaque EMPTY>
<!-- Affect busy time searches -->
<!ELEMENT transparent EMPTY>
<!-- Invisible to busy time searches -->
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Example:
<C:schedule-calendar-transp
xmlns:C="urn:ietf:params:xml:ns:caldav">
<C:opaque/>
</C:schedule-calendar-transp>
9.2. CALDAV:schedule-default-calendar-URL Property
Name: schedule-default-calendar-URL
Namespace: urn:ietf:params:xml:ns:caldav
Purpose: Specifies a default calendar for an Attendee where new
scheduling object resources are created.
Protected: This property MAY be protected in the case where a server
does not support changing the default calendar, or does not
support a default calendar.
COPY/MOVE behavior: This property is only defined on a scheduling
Inbox collection which cannot be moved or copied.
Description: This property MAY be defined on a scheduling Inbox
collection. If present, it contains zero or one DAV:href XML
elements. When a DAV:href element is present, its value indicates
a URL to a calendar collection that is used as the default
calendar. When no DAV:href element is present, it indicates that
there is no default calendar. In the absence of this property
there is no default calendar. When there is no default calendar
the server is free to choose the calendar in which a new
scheduling object resource is created. See Section 4.3.
Definition:
<!ELEMENT schedule-default-calendar-URL (DAV:href?)>
Example:
<C:schedule-default-calendar-URL xmlns:D="DAV:"
xmlns:C="urn:ietf:params:xml:ns:caldav">
<D:href>/home/cyrus/calendars/work/</D:href>
</C:schedule-default-calendar-URL>
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Internet-Draft CalDAV Scheduling Extensions April 20129.3. CALDAV:schedule-tag Property
Name: schedule-tag
Namespace: urn:ietf:params:xml:ns:caldav
Purpose: Indicates whether a scheduling object resource has had a
"consequential" change made to it.
Value: opaque-tag (defined in Section 3.11 of [RFC2616])
Protected: This property MUST be protected as only the server can
update the value.
COPY/MOVE behavior: This property value is determined by the server
and MAY be different from the value on source resource.
Description: The CALDAV:schedule-tag property MUST be defined on all
scheduling object resources. This property is described in
Section 3.2.10.
Definition:
<!ELEMENT schedule-tag (#PCDATA)>
Example:
<C:schedule-tag xmlns:C="urn:ietf:params:xml:ns:caldav"
>"12345-67890"</C:schedule-tag>
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Internet-Draft CalDAV Scheduling Extensions April 201211. Security Considerations
The process of scheduling involves the sending and receiving of
scheduling messages. As a result, the security problems related to
messaging in general are relevant here. In particular the
authenticity of the scheduling messages needs to be verified.
Servers and clients MUST use an HTTP connection protected with TLS as
defined in [RFC2818] for all scheduling operations. Clients MUST use
the procedures detailed in Section 6 of [RFC6125] to verify the
authenticity of the server. Servers MUST make use of HTTP
authentication [RFC2617] to verify the authenticity of the calendar
user for whom the client is sending requests.
11.1. Preventing Denial of Service Attacks
Servers MUST ensure that clients cannot consume excessive server
resources by carrying out "large" scheduling operations. In
particular, servers SHOULD enforce CALDAV:max-resource-size, CALDAV:
max-instances and CALDAV:max-attendees-per-instance pre-conditions as
applicable for scheduling Inbox and Outbox collections.
11.2. Verifying Scheduling Operations
When handling a scheduling operation:
1. Servers MUST verify that the principal associated with the DAV:
owner of the calendar collection in which a scheduling object
resource is being manipulated contains a CALDAV:schedule-outbox-
URL property value.
2. Servers MUST verify that the currently authenticated user has the
CALDAV:schedule-send privilege, or a sub-privilege aggregated
under this privilege, on the scheduling Outbox collection of the
DAV:owner of the calendar collection in which a scheduling object
resource is being manipulated.
3. Servers MUST only deliver scheduling messages to recipients when
the CALDAV:schedule-deliver privilege, or a sub-privilege
aggregated under this privilege, is granted on the recipient's
scheduling Inbox collection for the principal associated with the
DAV:owner of the calendar collection in which a scheduling object
resource is being manipulated.
4. To prevent impersonation of calendar users, the server MUST
verify that the "ORGANIZER" property in an organizer scheduling
object resource matches one of the calendar user addresses of the
DAV:owner of the calendar collection in which the resource is
stored.
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5. To prevent spoofing of an existing scheduling object resource,
servers MUST verify that the "UID" iCalendar property value in a
new scheduling object resource does not match that of an existing
scheduling object resource with a different "ORGANIZER" property
value.
11.3. Verifying Busy Time Information Requests
When handling a POST request on a scheduling Outbox collection:
1. Servers MUST verify that the principal associated with the
calendar user address specified in the "ORGANIZER" property of
the scheduling message data in the request contains a CALDAV:
schedule-outbox-URL property value that matches the scheduling
Outbox collection targeted by the request.
2. Servers MUST verify that the currently authenticated user has the
CALDAV:schedule-send privilege, or a sub-privilege aggregated
under this privilege, on the scheduling Outbox collection
targeted by the request.
3. Servers MUST only return valid freebusy information for
recipients when the CALDAV:schedule-deliver privilege, or a sub-
privilege aggregated under this privilege, is granted on the
recipient's scheduling Inbox collection for the principal
associated with the DAV:owner of the scheduling Outbox collection
targeted by the request.
11.4. Privacy Issues
This specification only defines how calendar users on the same server
are able to schedule with each other - unauthenticated users have no
way to carry out scheduling operations. Access control privileges
(as per Section 6) can control which of those users can schedule with
others. Calendar users not wishing to expose their calendar
information to other users can do so by denying privileges to
specific users, or all users, for all scheduling operations, or
perhaps only freebusy.
Attendees can also use the Schedule-Reply request header
(Section 8.1) with the value set to "F" to prevent notification to an
Organizer that a scheduling object resource was deleted. This allows
Attendees to remove unwanted scheduling messages without any response
to the Organizer.
Servers MUST NOT expose any private iCalendar data, or WebDAV
resource state information (URLs, WebDAV properties, etc) for one
calendar user to another via scheduling messages or error responses
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to scheduling operations. In particular, as per Section 8.1 of
[RFC4918], authorization errors MUST take preference over other
errors.
11.5. Mitigation of iTIP ThreatsSection 6.1 of iTIP [RFC5546] defines a set of potential threats in a
scheduling system, and in Section 6.2 defines recommendations on how
those can be addressed in protocols using iTIP. This specification
addresses the iTIP threats in the following manner:
Spoofing the Organizer Addressed by item 4 in Section 11.2.
Spoofing the Attendee Addressed by item 2 in Section 11.2 and
Section 3.2.2.1.
Unauthorized Replacement of the Organizer Addressed by item 5 in
Section 11.2.
Eavesdropping and Data Integrity Addressed by requiring TLS.
Flooding a Calendar Addressed by requirements in Section 11.1
Unauthorized REFRESH Requests This specification does not support
the REFRESH method.
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Internet-Draft CalDAV Scheduling Extensions April 2012Appendix B. Example Scheduling Operations
This section describes some example scheduling operations that give a
general idea of how scheduling is carried out between CalDAV clients
and servers from the perspective of meeting Organizers and Attendees.
The server is assumed to be hosted in the "example.com" domain, and
users whose email address is at the "example.com" domain are assumed
to be hosted by the server. In addition, the email addresses in the
"example.net" domain are also valid email addresses for calendar
users hosted by the server. Calendar users with an email address at
the "example.org" domain are assumed to not be hosted by the server.
In the following examples the requests and responses are incomplete
and are only for illustrative purposes. In particular, HTTP
authentication headers and behaviors are not shown, even though they
are required in normal operation.
B.1. Example: Organizer Inviting Multiple Attendees
In the following example, Cyrus invites Wilfredo, Bernard and Mike to
a single instance event by simply creating a new scheduling object
resource in one of his calendar collections by using the PUT method.
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will retrieve the event back from the server to get the schedule
status of the Organizer.
>> Request <<
GET /home/wilfredo/calendars/work/BB64861C2228.ics HTTP/1.1
Host: cal.example.com
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f. Relaxed MUST->MAY for Organizer setting PARTSTAT value.
g. Tweaked restrictions on Create/Modify to emphasize that 4791
restrictions also apply.
h. Added comment that 'opaque' is the default when the CALDAV:
schedule-calendar-transp property is not present.
i. Description of Schedule-Reply header changed to reflect that it
is only relevant for Attendees.
j. Minor typos fixed.
C.8. Changes in -05
This draft has changed substantially since the -04 version. The
primary reason for this change was implementation experience from a
number of vendors who implemented products based on the earlier
drafts. Experience showed that the client/server interaction was not
reliable in keeping scheduling messages synchronized between
organizer and attendees. In addition the latency in updates due to
clients being offline proved unacceptable to users. These issues led
to the redesign of this specification to support a server-based
processing model that eliminates all the problems seen previously.
Whilst this adds significant complexity to the server in that it
needs to be a full blown iTIP processing agent, it does remove a lot
of the same complexity from clients, opening up the possibility of
supporting complex scheduling behaviors even with "thin" clients.
In the judgement of the authors, we consider this new specification
to be a substantial improvement over the old one and believe it
represents a stronger protocol that will lead to better
interoperability.
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